1. Field of the Invention
The current invention relates to a probe measuring force adjuster.
2. Description of Related Art
In a coordinate measuring machine, a scanning measurement is performed by bringing a scanning probe into contact with a surface of a measured object (see, for example, Japanese Patent Laid-open Publication No. 2010-286475). When using an elastic hinge in a guide mechanism (in three axis directions of X, Y, Z) of the scanning probe, a measuring force of the probe is generated by a spring constant in a bending direction of the elastic hinge. The higher a rigidity of the guide mechanism is, the larger the spring constant becomes, and the larger the measuring force of the probe becomes. When the measuring force of the probe becomes large, certain influences are increased, such as an influence from a frictional force generated between a workpiece and a stylus during measurement and an influence from bending of the stylus mounted on the probe. As a result, highly accurate measurement becomes difficult.
By contrast, a technique of stabilizing the measuring force is known, in which fluctuation of the measuring force of the probe is inhibited by detecting and controlling the measuring force (Japanese Patent Laid-open Publication No. 2010-286475).
In addition, a technology is proposed for a measuring device using an elastic hinge mechanism in which a restoring characteristic of an elastic hinge is adjusted using magnets (Japanese Patent Laid-open Publication No. H11-141537).
However, inventors of the present invention have discovered an issue, as discussed below, with respect to the above-noted techniques. For example, in order to adjust the measuring force, the rigidity of the spring or the elastic hinge that provides the measuring force is lowered, and when the spring constant in the bending direction becomes small, the rigidity in another direction such as twisting or curving becomes lower as well. As a result, the influence of deformation other than in the bending direction due to the measuring force becomes greater and leads to deterioration in measurement accuracy. Accordingly, to achieve high accuracy of the scanning probe, a scanning probe with high rigidity in a direction other than a moveable direction and a small spring constant in the bending direction is required.
By contrast, in the technique disclosed in Japanese Patent Laid-open Publication No. 2010-286475, though the measuring force is adjustable, controlling the measuring force generates heat, which affects the form measuring machine in the form of thermal deformation and the like and leads to a decrease in measurement accuracy. In addition, electrical noise is generated by executing control of the measuring force, which leads to a further decrease in measurement accuracy. Furthermore, a need to mount a controller on the form measuring machine increases costs of the form measuring machine.